Most immunization strategies of current vaccines use protocols that prime and boost the immune system using a parenteral route e.g., intra-dermal, sub-cutaneous and intra-muscular. These means of immunization generate strong systemic immunity but little or no mucosal immunity. In addition, this traditional vaccination protocol, despite inducing both long-lived central memory T cells and short-lived effector T cells, does not sustain a reasonable pool of the latter. These cells, which express CD4 surface antigen and recognize antigenic peptides displayed on the surface of MHC II molecules are the main orchestrators of the immune response. The short-lived T helper cells influence the function of important effector cells including CD8 cytotoxic T cells, antibody producing B lymphocytes and macrophages all of which are important in generation of a successful immune response and subsequent memory.
The primary reason for using a mucosal route of vaccination is that most infections affect or start from a mucosal surface and that in these infections, topical application of a vaccine is often required to induce a protective immune response. Examples include gastrointestinal infections caused by Helicobacter pylori, Vibrio cholera, and Clostridium difficile; enterotoxigenic infections caused by Escherichia coli; respiratory infections caused by Mycobacterium tuberculosis and Mycoplasma pneumonia; and sexually transmitted genital infections caused by HIV, herpes simplex virus, and Chlamydia trachomatis. Therefore, a need exists for a vaccination method in which mucosal immunity is provided.
Yet a further need exists for using persistent and abundant commensal oral organisms to deliver antigens for mucosal immunization against infectious diseases. Yet a further need exists for a vaccination protocol that provides generation and maintenance of a significant pool of protective effector and memory T cells.